By Susanne von Rosenberg, UC Master Gardener of Napa County
Can you believe it's already September and we're headed into fall gardening season? It's time to assess what you would like to grow this autumn.
Now is the right time to plant cool-season vegetables, fall annual flowers and—as soon as the rains start—California native plants It's also the moment to plant spring-flowering bulbs.
I love bulbs because they are so easy to care for and add such beauty and joy to my garden. Bulbs to plant now include daffodils, crocus, many types of lilies, bearded iris and tulips. Plant freesia, canna, begonias, gladiolus, crocosmia and dahlias in late winter and early spring for summer bloom.
There are five major types of plants that we refer to as bulbs: true bulbs, corms, tubers, rhizomes and tuberous roots. Bulbs store food (in the form of carbohydrates) to support growth and flowering for the next growth cycle. Most are perennials, although some, such as hyacinths, can be short-lived. Bulbs initially produce leaves, followed by flowers. Bulbs need only a light application of fertilizer after the leaves emerge.
After flowering and the growing season end, bulbs typically go dormant and the plant dies down to the ground. For bulbs that flower in spring, the growing season lasts until late spring or early summer.To ensure that your bulbs continue flowering year after year, keep the leaves until they naturally die back or turn yellow. You can cut back dead flower stalks at the base at any time. After the plant flowers, its leaves continue to produce carbohydrates to store in the bulb.
Water as needed to keep the leaves alive for the rest of their growing season. (Too much water may cause the bulbs to mildew or rot.) After you remove the leaves, you can dig up the bulbs and store them in a cool, dark, dry place, or you can leave them in the ground. Some bulbs need to be divided regularly to keep flowering well. If you leave bulbs in the ground and they are not performing well, consider digging them up and dividing them.
Daffodils, tulips, lilies, amaryllis and hyacinths are all true bulbs. True bulbs are composed of a series of leaves modified for food storage. Onions and garlic are also bulbs; when you cut through an onion, the rings you see are the leaves. Garlic and lilies form a looser bulb. All true bulbs root from the bottom. If you're not quite sure which side is the bottom, plant the bulb sideways.
Corms are another common type of bulb. Instead of modified leaves, corms are modified stems. The bottom of a corm is actually the base of a stem. Corms are easy to confuse with true bulbs because they look a lot like them. To know whether you're looking at a true bulb or a corm, cut the bulb in half to view its internal structure. If it's solid, it's a corm. If you see rings, it's a true bulb.
Freesias, crocus, gladiolas, watsonia and my favorite, crocosmia, are corms, as are water chestnuts. Some corms, like freesias and watsonia, have a kind of furry covering. Buds are located on the tops of the corm, and roots and baby corms (cormels) grow from the bottom.
Tubers are also underground stems. They differ from corms in that they are not the base of the stem. Common flowering tubers include anemones, begonia and cyclamen. Tubers have nodes (on potatoes, we call them eyes) that can appear anywhere on the tuber and sprout both new shoots and new roots. Other tubers you might be familiar with include yams, turmeric and ginger. Tubers can grow in any direction.
Rhizomes are elongated bulbs that are a type of underground stem. Unlike tubers, they only grow horizontally. Calla lilies, cannas and bearded iris are examples of rhizomes. (Dutch iris is a true bulb.) Leaves and buds grow only from the top of a rhizome, and roots grow only from the bottom. Rhizomes can sometimes emerge above the surface of the soil, and rhizomatous bulbs should generally be planted shallowly.
The last major type of bulb is a tuberous root. Tuberous bulbs are thickened roots that radiate from a central stem. Agapanthus, society garlic, dahlias and day lilies have tuberous roots. The growth buds are at the base of old stems, not on the tuberous roots.
Different bulbs require different planting depths. Plant bearded iris just below the soil surface; plant tulips deeply, up to eight inches deep in loose soil. For recommended planting depth, consult your bulb source or a reputable online source. The Sacramento Master Gardener website has a great bulb-planting schedule that also provides information on planting depth and spacing.
Food Growing Forum: Napa CountyMaster Gardeners will present a discussion of “Culinary Herbs” on Sunday, September 12, from 3 p.m. to 4 p.m., via Zoom. Register here to receive the Zoom link.
Free Guided Tree Walk: Join Master Gardeners of Napa County for a tree walk in Fuller Park in Napa on Tuesday, September 14, from 10 a.m. to noon. Limited to 12 people per walk. COVID safety protocols will be followed. You will be asked health questions and asked to sign in. Face masks and social distancing are required. Register here.
Napa Library Talk: Napa County Master Gardeners will give a talk on “Replace Grass, Save Water and Get Cash” on Thursday, October 7, from 7 p.m. to 8 p.m. via Zoom. Learn how to replace your thirsty lawn without digging it up. Register here to receive the Zoom link.
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to firstname.lastname@example.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.
For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.
- Author: susanne von rosenberg
Planting Bulbs for Spring Flowers
by Susanne von Rosenberg, UC Master Gardener of Napa County
It's September, and it's obvious that the days are getting shorter and autumn is on the way. One of the most pleasurable activities in a fall garden is planting spring-flowering bulbs. Spring-flowering bulbs add color to a late winter and spring garden, and the right kinds of bulbs will naturalize and reward your efforts for many years.
While we commonly refer to them all as bulbs, these spring-flowering marvels are actually five different types: true bulbs (such as daffodils and tulips), rhizomes (such as bearded iris), corms (freesias and gladiolas are common examples), tubers (cannas and anemones) and tuberous roots (like day lilies and ranunculus).
You see the most common types, including daffodils, tulips, irises, day lilies, calla lilies, dahlias and gladiolas, in many local gardens. Tulips are the most difficult to grow locally because our winters do not provide enough chill, and because gophers adore tulip bulbs. If you want tulips in your landscape, the best approach is to think of them as annuals that you will need to replant every year. Grow them in pots or put them in protective cages if you plant them in the ground. Most other types of bulbs will regrow every year, provided they get the basic care they need.
First, plant them correctly. The best method will depend greatly on the bulb type. True bulbs should be planted at a depth of two to three times their diameter. Bearded iris rhizomes, on the other hand, should be planted with the top of the rhizome at or just below the soil surface.
If you buy bulbs at a nursery, ask the staff about proper care and planting instructions for the types you're buying. If you buy mail order, the delivery should be accompanied by planting instructions.
In our area, bulbs should be planted in October or November, when the soil temperature has dropped below 60°F. All bulbs do best in welldrained soil and should be watered well after planting. If our rainy season starts at the normal time, you won't need to do any additional watering. If rain is delayed or below normal, water the bulbs to give them about the same amount of water and with the same frequency as they would get in a normal year.
Most bulbs need full sun, but some, such as calla lilies, prefer partial shade. You can plant the earlier spring-flowering bulbs under deciduous trees; they will have finished blooming by the time the trees leaf out fully and cast too much shade.
To keep your bulbs performing well year after year, let the foliage die back naturally after bloom. Those produce food that is stored in the bulb to nourish next year's flowers. Also give them a light application of phosphate-heavy fertilizer (such as bone meal) every year. After three or four years, many types of bulbs become crowded and need to be divided. You can tell that it's time to divide them when you see a lot of leaves growing in a crowded area, but you get fewer flowers than in previous years.
Many bulbs native to the Cape Province of South Africa, which also has a Mediterranean climate, will do well here and naturalize easily. Try spraxia (also known as wand flower or harlequin flower), ixia or babiana. Another interesting variety to consider is rain lily, a Mexican native (Zephyranthes) that looks a bit like a crocus and comes in many colors.
You can also plant native bulbs this fall. One advantage of natives is that they bloom when native insects need them. They are also adapted to our climate and do not require any special soil preparation.
There are more than 200 species of native California bulbs, corms and rhizomes. Some examples include Coast iris, blue-eyed grass (a very small native iris), snake lily, camas bulbs and fritillaria. The Calflora website (www.calflora.org) lists 23 native species.
If you buy native bulbs, make sure they are ethically sourced, not collected from the wild but propagated by the nursery that sells them. Because native bulbs are likely to be more expensive, it's particularly important to be well-informed about the growing conditions they require.
For example, camas bulbs prefer soil that is very moist in the spring and then dries out, conditions typical of seasonal wetlands and the edges of creeks. Give them a home in an area of your garden that is soggy during the wet season, but then dries out. They have a long flowering period (typically April through June).
Camas bulbs were used as a food source by native American tribes and are very appealing to gophers. They are one of the few native bulbs that need gopher protection. California native bulbs are a worthy addition to a native garden and also make great potted plants.
Next workshop: “Stinking Roses and Edible Alliums: Grow These Essentials for Your Kitchen” on Saturday, October 12, from 9:30 to 11:30 a.m., at the University of California Cooperative Extension, 1710 Soscol Avenue, Napa. For more details and online registration go to http://napamg.ucanr.edu or call 707-253-4221.
The UC Master Gardeners are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website (http://napamg.ucanr.edu) or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.